EP2998651B1

EP2998651B1 - Boiler and method for operating boiler

Info

Publication number: EP2998651B1
Application number: EP15185739.8A
Authority: EP
Inventors: Keigo Matsumoto; Kazuhiro Domoto; Naofumi Abe; Jun Kasai
Original assignee: Mitsubishi Heavy Industries Ltd
Current assignee: Mitsubishi Heavy Industries Ltd
Priority date: 2011-04-01
Filing date: 2012-03-07
Publication date: 2019-01-09
Anticipated expiration: 2032-03-07
Also published as: EP3015766A1; MX2013011125A; EP2696139A1; CN103443543A; PL2995857T3; MX354825B; TWI531762B; US20170045221A1; US20160356490A1; KR101500921B1; US20160356489A1; US20140011141A1; EP2998651A1; CN103443543B; MX357868B; EP2995857A1; KR101547083B1; ES2738321T3; EP3018407A1; KR20150068499A

Description

Field

The present invention relates to a boiler that produces steam by burning solid fuel and air, and a method for operating the boiler.

Background

For example, a conventional pulverized-coal-combustion boiler includes a furnace which is formed in a hollow shape and is provided in the vertical direction, and plural combustion burners are disposed in a furnace wall in the circumferential direction and are disposed at plural stages in the up and down direction. A fuel-air mixture obtained by mixing primary air with pulverized coal (fuel) formed by milling coal is supplied to the combustion burners, and hot secondary air is supplied to the combustion furnaces so that the fuel-air mixture and the secondary air blow into the furnace. Accordingly, a flame is generated, and hence the fuel-air mixture may be burned inside the furnace by the flame. Then, a flue gas duct is connected to the upper portion of the furnace, and the flue gas duct is equipped with a superheater, a reheater, an economizer, and the like for collecting the heat of a flue gas. Thus, steam may be produced by the heat exchange between water and the flue gas produced by the combustion in the furnace.
As such a pulverized-coal-combustion boiler or such a combustion burner, for example, pulverized-coal-combustion boilers or combustion burners disclosed in JP 08-135919A , JP 2006-189188A , JP 8-296815A , JP 9-203505A , JP 2006-057903A and JP 2008-145007A are known.
JP 3-009370B2 discloses a boiler with a furnace, a heat exchanger, a fuel nozzle for blowing a pulverized fuel and primary air into the furnace, a secondary air nozzle and a tertiary air nozzle for blowing secondary air and tertiary air into the furnace, and an additional air nozzle for blowing additional air into the furnace. The amount of additional air injected into the furnace is fixed with respect to the combustion burner total amount of air. Due to the structure of the nozzles the primary air, the secondary air and the tertiary air are injected in the form of swirled flows.
US 5764535B discloses another example of a pulverized coal combustion furnace.

Summary

Technical Problem

In the above-described conventional combustion burner, when a fuel gas obtained by mixing pulverized coal with air collides with a flame stabilizer, a separation of a flow occurs at a rear end portion of the flame stabilizer, and hence it is difficult to sufficiently exhibit the flame stabilization ability at the front end portion of the flame stabilizer. Further, in the conventional boiler, since the pulverized coal contains moisture or a volatile content, operation parameters need to be adjusted based on the operation output of the boiler. In this case, it is difficult to directly set the operation parameters from the characteristics of the coal.
It is an object of the invention to provide a boiler and a method for operating the boiler capable of improving operation efficiency by appropriately burning solid fuel and a volatile content contained in the solid fuel.

Solution to Problem

According to the present invention, a boiler with the features of claim 1 is provided which inter alia includes: a furnace that burns solid fuel and air; a heat exchanger that collects heat by a heat exchange inside the furnace; a fuel nozzle that is able to blow a fuel gas obtained by mixing solid fuel with primary air into the furnace; a secondary air nozzle that is able to blow secondary air from the outside of the fuel nozzle to the furnace; an additional air nozzle that is able to blow additional air to the upside of the fuel nozzle and the secondary air nozzle in the furnace; an air amount adjusting device that is able to adjust the amount of the air supplied to the fuel nozzle, the secondary air nozzle, and the additional air nozzle; and a control device that controls the air amount adjusting device in response to a volatile content of the solid fuel.
Accordingly, since the control device controls the air amount adjusting device in response to the volatile content of the solid fuel so that the air amount adjusting device adjusts the amount of the air supplied to the fuel nozzle, the secondary air nozzle, and the additional air nozzle, the primary air amount, the secondary air amount, and the additional air amount are adjusted in response to the volatile content of the solid fuel. Accordingly, the volatile content of the solid fuel may be appropriately burned and the solid fuel may be appropriately burned. Thus, the production of the NOx or the unburned combustible content is suppressed, and hence the boiler operation efficiency may be improved.
In the boiler, the control device controls the air amount adjusting device in response to the volatile content of the solid fuel so as to adjust a distribution of the total air amount of the primary air and the secondary air and the air amount of the additional air.
Accordingly, the total air amount of the primary air and the secondary air is the air amount necessary for burning the volatile content of the solid fuel, and the total air amount of the primary air and the secondary air changes in response to the volatile content of the solid fuel. Thus, the volatile content of the solid fuel may be appropriately burned.
In the boiler, the furnace is equipped with a tertiary air nozzle that is able to blow tertiary air from the outside of the secondary air nozzle, and the control device controls the air amount adjusting device in response to the volatile content of the solid fuel so as to adjust a distribution of the total air amount of the primary air and the secondary air and the total air amount of the tertiary air and the additional air.
Accordingly, since the total air amount of the primary air and the secondary air changes, the volatile content of the solid fuel may be appropriately burned.
Advantageously, in the boiler, the control device controls the air amount adjusting device so that the primary air amount and the additional air amount become a predetermined air amount, and adjusts a distribution of the secondary air and the tertiary air in response to the volatile content of the solid fuel.
Accordingly, since the primary air is the transportation air for transporting the solid fuel and the additional air completely burns the solid fuel so as to suppress the production of NOx, the primary air and the additional air are set as the predetermined air amounts, and the distribution of the secondary air and the tertiary air is adjusted in response to the volatile content of the solid fuel. Thus, the solid fuel and the volatile content thereof may be appropriately burned while maintaining a predetermined fuel-air ratio.
Advantageously, in the boiler, the control device increases a distribution of the secondary air when the volatile content of the solid fuel increases.
Accordingly, since the secondary air is the combustion air mixed with the fuel gas so as to burn the solid fuel, the solid fuel and the volatile content thereof may be appropriately burned by increasing the distribution of the secondary air when the volatile content of the solid fuel increases.
According to the present invention, a method for operating a boiler with the features of claim 5 is provided, wherein the boiler includes inter alia a furnace that burns solid fuel and air, a heat exchanger that collects heat by a heat exchange inside the furnace, a fuel nozzle that is able to blow a fuel gas obtained by mixing solid fuel with primary air to the furnace, a secondary air nozzle that is able to blow secondary air from the outside of the fuel nozzle into the furnace, and an additional air nozzle that is able to blow additional air to the upside of the fuel nozzle and the secondary air nozzle in the furnace. A distribution of the secondary air and the tertiary air is adjusted in response to a volatile content of the solid fuel.
Accordingly, since the distribution of the secondary air and the tertiary air is adjusted in response to the volatile content of the solid fuel, the volatile content of the solid fuel may be appropriately burned and the solid fuel may be appropriately burned. Thus, the production of the NOx or the unburned combustible content is suppressed, and hence the boiler operation efficiency may be improved.
Advantageously, in the method for operating the boiler, the distribution of the secondary air increases when the volatile content of the solid fuel increases.
Accordingly, since the secondary air is the combustion air mixed with the fuel gas so as to burn the solid fuel, the solid fuel and the volatile content thereof may be appropriately burned by increasing the distribution of the secondary air when the volatile content of the solid fuel increases.

Advantageous Effects of Invention

According to the boiler and the method for operating the boiler of the invention, since the distribution of the secondary air and the tertiary air and the additional air, and the like is adjusted in response to the volatile content of the solid fuel, it is possible to improve the operation efficiency by appropriately burning the solid fuel and the volatile content contained in the solid fuel.

Brief Description of Drawings

FIG. 1 is a schematic configuration diagram illustrating a pulverized-coal-combustion boiler as a boiler according to an embodiment of the invention.
FIG. 2 is a plan view illustrating a combustion burner of the pulverized-coal-combustion boiler of the embodiment.
FIG. 3 is a front view illustrating the combustion burner of the embodiment.
FIG. 4 is a cross-sectional view illustrating the combustion burner of the embodiment.
FIG. 5 is a graph illustrating a NOx production amount and an unburned combustible content production amount with respect to primary air and secondary air.

Description of Embodiments

Hereinafter, preferred embodiments of a boiler and a method for operating the boiler of the invention will be described in detail with reference to the accompanying drawings. Embodiment
In the pulverized-coal-combustion boiler, the pulverized coal (coal) is used as the solid fuel. In this case, the coal contains moisture or a volatile content, and the amount of moisture changes in accordance with the type thereof. For this reason, there is a need to control the operation of the boiler in response to the volatile content or the moisture contained in the coal.
As the control of the operation of the boiler in consideration of the volatile content of the coal, for example, the control disclosed in JP 08-135919A , JP 2006-189188A , JP 8-296815A , JP 9-203505A , JP 2006-057903A and JP 2008-145007A is known. In the pulverized coal burner and the boiler using the same disclosed in JP 2006-057903A , there are provided the pulverized coal fuel-air mixture passage that ejects the pulverized coal fuel-air mixture obtained by mixing the pulverized coal with the transportation air and the hot gas supply passage that ejects a hot gas with a low oxygen concentration at a high temperature effective for the discharge of the volatile content of the pulverized coal. Further, in the coal-combustion boiler disclosed in JP 2008-145007A , there are provided a temperature detector that detects the temperature of the primary air for supplying the pulverized coal to the coal-combustion boiler, the primary air temperature adjusting unit that adjusts the temperature of the primary air, and the control device that controls the primary air temperature adjusting unit so that the temperature of the primary air becomes a predetermined temperature based on the detection result of the temperature detector.
In the conventional boiler, the entire pulverized coal is heated so as to adjust the moisture or the volatile content, and is burned inside the furnace. In this case, the operation parameter needs to be adjusted based on the operation output of the boiler, and it is difficult to directly set the operation parameter based on the characteristics of the coal.
The invention is made to solve the above-described problems, and it is an object of the invention to provide a boiler and a method for operating the boiler capable of improving an operation efficiency by appropriately burning solid fuel and a volatile content contained in the solid fuel.
FIG. 1 is a schematic configuration diagram illustrating a pulverized-coal-combustion boiler as a boiler according to a seventeenth embodiment of the invention, FIG. 2 is a plan view illustrating a combustion burner of the pulverized-coal-combustion boiler of the seventeenth embodiment, FIG. 3 is a front view illustrating the combustion burner of the seventeenth embodiment, FIG. 4 is a cross-sectional view illustrating the combustion burner of the seventeenth embodiment, and FIG. 5 is a graph illustrating a NOx production amount and an unburned combustible content production amount with respect to the primary air and the secondary air.
The pulverized-coal-combustion boiler that employs the combustion burner of the seventeenth embodiment is a boiler capable of collecting the heat generated by the combustion by burning the pulverized coal obtained by milling the coal as the solid fuel and burning the pulverized coal through the combustion burner.
In the embodiment, as illustrated in FIG. 1, a pulverized-coal-combustion boiler 510 is a conventional boiler, and includes a furnace 511 and a combustion device 512. The furnace 511 is formed in a hollow square cylindrical shape, and is provided in the vertical direction. Then, the combustion device 512 is provided in the lower portion of the furnace wall forming the furnace 511.
The combustion device 512 includes plural combustion burners 521, 522, 523, 524, and 525 which are attached to the furnace wall. In the embodiment, the combustion burners 521, 522, 523, 524, and 525 are disposed as one set in the circumferential direction at four equal intervals therebetween, and five sets, that is, five stages are disposed in the vertical direction.
Then, the respective combustion burners 521, 522, 523, 524, and 525 are connected to coal pulverizers (mills) 531, 532, 533, 534, and 535 through pulverized coal supply pipes 526, 527, 528, 529, and 530. Although not illustrated in the drawings, the coal pulverizers 531, 532, 533, 534, and 535 have a configuration in which milling tables are supported in a rotational driving state with rotation axes along the vertical direction inside a housing and plural milling rollers are provided while facing the upper sides of the milling tables and are supported so as to be rotatable along with the rotation of the milling tables. Accordingly, when coal is input between plural milling rollers and plural milling tables, the coal is milled into a predetermined size therein. Thus, pulverized coal which is classified by transportation air (primary air) may be supplied from pulverized coal supply pipes 526, 527, 528, 529, and 530 to the combustion burners 521, 522, 523, 524, and 525.
Further, in the furnace 511, wind boxes 536 are provided at the attachment positions of the respective combustion burners 521, 522, 523, 524, and 525, where one end portion of an air duct 537 is connected to the wind box 536 and an air blower 538 is attached to the other end portion of the air duct 537. Moreover, in the furnace 511, an additional air nozzle 539 is provided above the attachment positions of the respective combustion burners 521, 522, 523, 524, and 525, and an end portion of an air duct 540 branched from the air duct 537 is connected to the additional air nozzle 539. Accordingly, the combustion air (the secondary air and the tertiary air) sent from the air blower 538 is supplied from the air duct 537 to the wind box 536 so as to be supplied from the wind boxes 36 to the respective combustion burners 521, 522, 523, 524, and 525 and to be supplied from the branched air duct 540 to the additional air nozzle 539.
For this reason, in the combustion device 512, the respective combustion burners 521, 522, 523, 524, and 525 may blow a pulverized fuel-air mixture (fuel gas) obtained by mixing pulverized coal and primary air into the furnace 511 and may blow secondary air and tertiary air into the furnace 511. Then, a flame may be formed by igniting the pulverized fuel-air mixture through an ignition torch (not illustrated).
Further, the pulverized coal supply pipes 526, 527, 528, 529, and 530 are equipped with flowrate adjustment valves 541, 542, 543, 544, and 545 capable of adjusting the pulverized fuel-air mixture amount, the air duct 537 is equipped with a flowrate adjustment valve 546 capable of adjusting the amount of the combustion air (the secondary air and the tertiary air), and the branched air duct 540 is equipped with a flowrate adjustment valve 547 capable of adjusting the additional air amount. Then, a control device 548 may adjust the opening degrees of the respective flowrate adjustment valves 541, 542, 543, 544, 545, 546, and 547. In this case, the pulverized coal supply pipes 526, 527, 528, 529, and 530 may not be equipped with the flowrate adjustment valves 541, 542, 543, 544, and 545.
Furthermore, when generally activating the boiler, the respective combustion burners 521, 522, 523, 524, and 525 form a flame by ejecting oil fuel into the furnace 511.
A flue gas duct 550 is connected to the upper portion of the furnace 511, and the flue gas duct 550 is equipped with superheaters 551 and 552, reheaters 553 and 554, and economizers 555, 556, and 557 as convection heat transfer portions for collecting the heat of the flue gas. Accordingly, a heat exchange is performed between water and a flue gas that is produced by the combustion in the furnace 511.
The downstream side of the flue gas duct 550 is connected with a flue gas pipe 558 into which the flue gas subjected to the heat exchange is discharged. An air heater 559 is provided between the flue gas pipe 558 and the air duct 557, and a heat exchange is performed between the air flowing through the air duct 537 and the flue gas flowing through the flue gas pipe 558, so that the temperature of the combustion air supplied to the combustion burners 521, 522, 523, 524, and 525 may be increased.
Furthermore, although not illustrated in the drawings, the flue gas pipe 558 is equipped with a denitration device, an electronic precipitator, an inducing air blower, and a desulfurization device, and the downstream end portion thereof is equipped with a stack.
Accordingly, when the coal pulverizers 531, 532, 533, 534, and 535 are driven, pulverized coal produced therein is supplied along with the transportation air to the combustion burners 521, 522, 523, 524, and 525 through the pulverized coal supply pipes 526, 527, 528, 529, and 530. Further, the heated combustion air is supplied from the air duct 537 to the respective combustion burners 521, 522, 523, 524, and 525 through the wind boxes 536, and is supplied from the branched air duct 540 to the additional air nozzle 539. Then, the combustion burners 521, 522, 523, 524, and 525 blow the pulverized fuel-air mixture obtained by mixing the pulverized coal, the transportation air to the furnace 511 and blow the combustion air to the furnace 511, and ignite the pulverized fuel-air mixture and the air at this time so as to form a flame. Further, the additional air nozzle 539 may perform the combustion control by blowing the additional air to the furnace 511. In the furnace 511, when a flame is generated by the combustion of the pulverized fuel-air mixture and the combustion air and the flame is generated at the lower portion inside the furnace 511, the combustion gas (the flue gas) rises inside the furnace 511, and is discharged to the flue gas duct 550.
Furthermore, the inside of the furnace 511 is maintained at the reduction atmosphere in a manner such that the air supply amount with respect to the pulverized coal supply amount becomes smaller than the theoretical air amount. Then, when NOx produced by the combustion of the pulverized coal is reduced in the furnace 511 and additional air is additionally supplied thereto, the oxidization combustion of the pulverized coal is completed and hence the production amount of NOx caused by the combustion of the pulverized coal is reduced.
At this time, water supplied from a water feeding pump (not illustrated) is preheated by the economizers 555, 556, and 557, is supplied to a steam drum (not illustrated), and heated while being supplied to the respective water pipes (not illustrated) of the furnace wall so as to become saturated steam. Then the saturated steam is transported to a steam drum (not illustrated). Further, the saturated steam of the steam drum (not illustrated) is introduced into the superheaters 551 and 552 and is superheated by the combustion gas. The superheated steam produced by the superheaters 551 and 552 is supplied to a power generation plant (not illustrated) (for example, a turbine or the like). Further, the steam which is extracted during the expanding process in the turbine is introduced into the reheaters 553 and 554, is superheated again, and is returned to the turbine. Furthermore, the furnace 511 of a drum type (steam drum) has been described, but the invention is not limited to the structure.
Subsequently, a harmful substance such as NOx is removed from the flue gas which passes through the economizers 555, 556, and 557 of the flue gas duct 550 by a catalyst of a denitration device (not illustrated) in the flue gas pipe 558, a particulate substance is removed therefrom by the electronic precipitator, and a sulfur content is removed therefrom by the desulfurization device. Then, the flue gas is discharged to the atmosphere through the stack.
Here, the combustion device 512 will be described in detail, but since the respective combustion burners 521, 522, 523, 524, and 525 constituting the combustion device 512 have substantially the same configuration, only the combustion burner 521 that is positioned at the uppermost stage will be described.
As illustrated in FIG. 2, the combustion burner 521 includes the combustion burners 521a, 521b, 521c, and 521d which are provided at four wall surfaces of the furnace 511. The respective combustion burners 521a, 521b, 521c, and 521d are connected with respective branch pipes 526a, 526b, 526c, and 526d which are branched from a pulverized coal supply pipe 526, and are connected with respective branch pipes 537a, 537b, 537c, and 537d branched from the air duct 537.
Accordingly, the respective combustion burners 521a, 521b, 521c, and 521d which are positioned at the respective wall surfaces of the furnace 511 blow the pulverized fuel-air mixture obtained by mixing the pulverized coal and the transportation air to the furnace 511 and blow the combustion air to the outside of the pulverized fuel-air mixture. Then, the pulverized fuel-air mixture is ignited from the respective combustion burners 521a, 521b, 521c, and 521d, so that four flames F1, F2, F3, and F4 may be formed. The flames F1, F2, F3, and F4 become a flame swirl flow that turns in the counterclockwise direction when viewed from the upside of the furnace 511 (in FIG. 2).
As illustrated in FIGS. 3 and 4, in the combustion burner 521 (521a, 521b, 521c, 521d) with such a configuration, the combustion burner is equipped a fuel nozzle 561, a secondary air nozzle 562, and a tertiary air nozzle 563 from the center side thereof and is equipped with a flame stabilizer 564. The fuel nozzle 561 may blow the fuel gas (the pulverized fuel-air mixture) obtained by mixing the pulverized coal (the solid fuel) with the transportation air (the primary air). The secondary air nozzle 562 is disposed at the outside of the first nozzle 561 and may blow the combustion air (the secondary air) to the outer peripheral side of the fuel gas ejected from the fuel nozzle 561. The tertiary air nozzle 563 is disposed at the outside of the secondary air nozzle 562, and may blow the tertiary air to the outer peripheral side of the secondary air ejected from the secondary air nozzle 562.
Further, the flame stabilizer 564 is disposed inside the fuel nozzle 561 so as to be positioned at the downstream side of the fuel gas blowing direction and near the axis center, and serves to ignite and stabilize the fuel gas. The flame stabilizer 564 is formed in a so-called double cross split structure in which two flame stabilizing members following the horizontal direction and two flame stabilizing members following the vertical direction (the up and down direction) are disposed in a cross shape. Then, in the flame stabilizer 564, the widened portions are formed in the front end portions of the respective flame stabilizing members (the downstream end portions in the fuel gas flowing direction).
For this reason, each of the fuel nozzle 561 and the secondary air nozzle 562 has an elongated tubular shape, the fuel nozzle 561 includes a rectangular opening portion 561a, and the secondary air nozzle 562 includes a rectangular annular opening portion 562a. Thus, the fuel nozzle 561 and the secondary air nozzle 562 are formed in a double tube structure the tertiary air nozzle 563 is disposed as a double tube structure at the outside of the fuel nozzle 561 and the secondary air nozzle 562, and includes a rectangular annular opening portion 563a. As a result, the opening portion 562a of the secondary air nozzle 562 is disposed at the outside of the opening portion 561a of the fuel nozzle 561, and the opening portion 563a of the tertiary air nozzle 563 is disposed at the outside of the opening portion 562a of the secondary air nozzle 562.
In the nozzles 561, 562, and 563, the opening portions 561a, 562a, and 563a are disposed so as to be flush with one another. Further, the flame stabilizer 564 is supported by the inner wall surface of the fuel nozzle 561 or a plate member (not illustrated) from the upstream side of the passage through which the fuel gas flows. Further, since plural flame stabilizing members are disposed as the flame stabilizer 564 inside the fuel nozzle 561, the fuel gas passage is divided into nine segments. Then, in the flame stabilizer 564, the widened portion of which the width is wide is positioned at the front end portion thereof, and the front end surface of the widened portion is disposed so as to be flush with the opening portion 561a.
Further, in the combustion burner 521, the fuel nozzle 561 is connected to the pulverized coal supply pipe 526 from the coal pulverizer 531. The secondary air nozzle 562 is connected with one connection duct 566 branched from the air duct 537 from the air blower 538, and the tertiary air nozzle 563 is connected with the other connection duct 567 branched from the air duct 537. A flowrate adjustment valve (a three-way valve or a damper) 568 is attached to the branch portions of the respective connection ducts 566 and 567 from the air duct 537. Then, the control device 548 (see FIG. 1) may adjust the opening degree of the flowrate adjustment valve 568, and may adjust the distribution of the air to the respective connection ducts 566 and 567.
Accordingly, in the combustion burner 521, the fuel gas obtained by mixing the pulverized coal with the primary air blows from the opening portion 561a of the fuel nozzle 561 into the furnace, the secondary air blows from the opening portion 562a of the secondary air nozzle 562 to the outside thereof, and the tertiary air blows from the opening portion 563a of the tertiary air nozzle 563 to the outside thereof. At this time, the fuel gas is branched at the opening portion 561a of the fuel nozzle 561 by the flame stabilizer 564, and is ignited and burned so as to become a fuel gas. Further, since the secondary air blows to the outer periphery of the fuel gas, the combustion of the fuel gas is promoted. Further, since the tertiary air blows to the outer periphery of the combustion flame, the outer peripheral portion of the combustion flame is cooled.
Then, since the flame stabilizer 564 is formed in a split shape in the combustion burner 521, the fuel gas is divided by the flame stabilizer 564 at the opening portion 561a of the fuel nozzle 561. At this time, the flame stabilizer 564 is disposed at the center zone of the opening portion 561a of the fuel nozzle 561, and the fuel gas is ignited and stabilized at the center zone. Thus, the inner flame stabilization of the combustion flame (the flame stabilization at the center zone of the opening portion 561a of the fuel nozzle 561) is realized.
For this reason, compared to the configuration in which the outer flame stabilization of the combustion flame is performed, the temperature of the outer peripheral portion of the combustion flame becomes low, and hence the temperature of the outer peripheral portion of the combustion flame under the high oxygen atmosphere by the secondary air may become low. Thus, the NOx production amount at the outer peripheral portion of the combustion flame is reduced.
Further, since the combustion burner 521 employs a configuration in which the inner flame stabilization is performed, it is desirable to supply the fuel gas and the combustion air (the secondary air and the tertiary air) as a straight flow. That is, it is desirable that the fuel nozzle 561 have a structure in which the secondary air nozzle 562 and the tertiary air nozzle 563 supply the fuel gas, the secondary air, and the tertiary air as a straight flow instead of a swirl flow. Since the fuel gas, the secondary air, and the tertiary air are ejected as the straight flow so as to form the combustion flame, the circulation of the gas inside the combustion flame is suppressed in the configuration in which the inner flame stabilization of the combustion flame is performed. Accordingly, the outer peripheral portion of the combustion flame is maintained in a low temperature, and the NOx production amount caused by the mixture with the secondary air is reduced.
Incidentally, in the pulverized-coal-combustion boiler 510 of the embodiment, the pulverized coal (coal) is used as the solid fuel, and the pulverized coal contains the volatile content. Accordingly, the combustion state becomes different due to the volatile content.
Therefore, in the pulverized-coal-combustion boiler 510 of the embodiment, as illustrated in FIGS. 1 and 4, since the control device 548 may adjust the fuel gas amount, the secondary air amount, the tertiary air amount, and the additional air amount by changing the opening degrees of the respective flowrate adjustment valves 541, 542, 543, 544, 545, 546, 547, and 568, the fuel gas amount, the secondary air amount, the tertiary air amount, and the additional air amount are adjusted in response to the volatile content of the pulverized coal.
In this case, it is desirable that the control device 548 adjust the distribution of the total air amount of the primary air and the secondary air and the air amount of the additional air in response to the volatile content of the pulverized coal. Specifically, the distribution of the total air amount of the primary air and the secondary air and the total air amount of the tertiary air and the additional air is adjusted.
In the embodiment, since the primary air amount and the additional air amount are predetermined air amounts, the control device 548 adjusts the distribution of the secondary air and the tertiary air in response to the volatile content of the pulverized coal. Then, the control device 548 increases the distribution of the secondary air when the volatile content of the pulverized coal increases.
That is, since the fuel nozzle 561 blows the fuel gas obtained by mixing the pulverized coal with the primary air into the furnace 511 and the primary air is the transportation air for the pulverized coal, the distribution of the primary air and the pulverized coal of the fuel gas, that is, the primary air amount is determined by the coal pulverizers 531, 532, 533, 534, and 535. Further, the additional air nozzle 539 performs oxidization combustion by inputting the combustion air to the combustion performed by the combustion burners 521, 522, 523, 524, and 525 to thereby completely perform the combustion. Here, since the additional air from the additional air nozzle 539 strengthens the reduction atmosphere in the main combustion zone and reduces the NOx discharge amount, the additional air amount for each boiler is determined.
Meanwhile, the secondary air nozzle 562 is used to blow the air as the secondary air passing from the air duct 537 to the connection duct 566 into the furnace 511, and the air is mainly used as the combustion air which is burned while being mixed with the fuel gas blowing from the fuel nozzle 561. The tertiary air nozzle 563 is used to blow the air as the tertiary air passing from the air duct 537 to the connection duct 566 into the furnace 511, and the air is mainly used as the additional air with respect to the combustion flame as in the additional air nozzle 359.
For this reason, the control device 548 changes the opening degree of the flowrate adjustment valve 568 so as to adjust the distribution of the total air amount of the primary air and the secondary air and the total air amount of the tertiary air and the additional air, that is, the distribution of the air amounts of the secondary air and the tertiary air, and hence handle a change in the volatile content of the pulverized coal. Here, when the volatile content of the pulverized coal increases, the control device 548 decreases the tertiary air amount and increases the secondary air amount so as to change the distribution of the secondary air and the tertiary air.
Here, as illustrated in FIG. 5, when the total air amount of the primary air and the secondary air increases, the NOx production amount increases and the unburned combustible content production amount decreases. That is, in the combustion burners 521, 522, 523, 524, and 525, the volatile content of the pulverized coal is mainly burned at the ignition portion (the vicinity of the opening portion 551a of the fuel nozzle 551). Then, when the air amount therein excessively increases, the NOx production amount increases. On the other hand, when the air amount therein is not sufficient, the pulverized coal is not smoothly burned, and the unburned combustible content production amount increases. For this reason, in the combustion burners 521, 522, 523, 524, and 525, there is a need to set the air amount as the amount in which the NOx production amount and the unburned combustible content production amount are suppressed to be low in consideration of the volatile content of the pulverized coal at the ignition portion.
Furthermore, the volatile content of the pulverized coal is measured before the coal is input to the respective coal pulverizers 531, 532, 533, 534, and 535, and the volatile content is stored as data in the control device 548. Further, since the distribution ratio of the secondary air and the tertiary air with respect to the volatile content of the pulverized coal becomes different depending on the type of the boiler or the combustion types of the combustion burners 521, 522, 523, 524, and 525, the distribution ratio is set in advance by an experiment. For example, a map is prepared, and is stored in the control device 548.
Accordingly, in the combustion burners 521, 522, 523, 524, and 525, the fuel gas blows from the fuel nozzle 561 to the furnace 511, the secondary air blows from the secondary air nozzle 562 to the furnace, and the tertiary air blows from the tertiary air nozzle 563 to the furnace. At this time, the fuel gas is ignited and burned by the flame stabilizer 564, and is further burned while being mixed with the secondary air. At this time, the main combustion zone is formed inside the furnace 511. Then, since the tertiary air blows from the tertiary air nozzle 563 to the main combustion zone, the outer peripheral portion of the combustion flame is cooled and the combustion thereof is promoted. Subsequently, the additional air nozzle 539 blows the additional air to the furnace 511 so as to perform the combustion control.
That is, in the furnace 511, the combustion gas which is obtained by the combustion of the fuel gas from the fuel nozzles 561 of the combustion burners 521, 522, 523, 524, and 525 and the secondary air from the secondary air nozzle 562 becomes less than a theoretical air amount, and the inside of the furnace is maintained at the reduction atmosphere. Then, the NOx which is produced by the combustion of the pulverized coal is reduced by the tertiary air. Subsequently, the oxidization combustion of the pulverized coal is completed by the additional air, and the NOx production amount caused by the combustion of the pulverized coal is reduced.
At this time, the control device 548 obtains the distribution ratio of the secondary air and the tertiary air in the combustion burners 521, 522, 523, 524, and 525 based on the volatile content of the pulverized coal measured in advance and the previously stored distribution ratio map of the secondary air and the tertiary air with respect to the volatile content of the pulverized coal, and sets the opening degree of the flowrate adjustment valve 568. Then, the control device 548 adjusts the opening degree of the flowrate adjustment valve 568 based on the set opening degree. Then, in the combustion burners 521, 522, 523, 524, and 525, the secondary air amount from the secondary air nozzle 562 and the tertiary air amount from the tertiary air nozzle 563 become optimal for the volatile content of the pulverized coal, and hence the pulverized coal and the volatile content are appropriately burned.
In this way, the boiler of the seventeenth embodiment includes the furnace 511 which burns the pulverized coal and the air, the superheaters 551 and 552 which collect heat by the heat exchange inside the furnace 511, the fuel nozzle 561 which is able to blow the fuel gas obtained by mixing the pulverized coal with the primary air to the furnace 511, the secondary air nozzle 562 which is able to blow the secondary air to the furnace 511, the tertiary air nozzle 563 which is able to blow the tertiary air to the furnace 511, the additional air nozzle 539 which is able to blow the additional air to the upper side of the fuel nozzle 561 and the secondary air nozzle 562 in the furnace 511, the flowrate adjustment valve 568 which performs the distribution of the secondary air amount and the tertiary air amount, and the control device 548 which controls the opening degree of the flowrate adjustment valve 568 in response to the volatile content of the pulverized coal.
Accordingly, since the control device 548 adjusts the distribution of the air amount of the secondary air nozzle 562 and the air amount of the tertiary air nozzle 563 by controlling the opening degree of the flowrate adjustment valve 568 in response to the volatile content of the pulverized coal, the secondary air amount and the tertiary air amount are adjusted in response to the volatile content of the pulverized coal. Accordingly, the volatile content of the pulverized coal may be appropriately burned, and the pulverized coal may be appropriately burned. Thus, the production of the NOx or the unburned combustible content may be suppressed, and hence the boiler operation efficiency may be improved. Further, the pulverized coal and the volatile content thereof may be appropriately burned while maintaining a predetermined fuel-air ratio.
Further, in the boiler of the seventeenth embodiment, the control device 548 increases the distribution of the secondary air when the volatile content of the pulverized coal increases. Since the secondary air is the combustion air which burns the pulverized coal while being mixed with the fuel gas, the distribution of the secondary air increases when the volatile content of the pulverized coal increases, so that the pulverized coal and the volatile content thereof may be appropriately burned.
Further, in the method for operating the boiler of the seventeenth embodiment, the distribution of the secondary air and the tertiary air is adjusted in response to the volatile content of the pulverized coal in the pulverized-coal-combustion boiler 510. Accordingly, the volatile content of the pulverized coal may be appropriately burned, and the pulverized coal may be appropriately burned. Thus, the production of the NOx or the unburned combustible content may be suppressed, and hence the boiler operation efficiency may be improved.
Furthermore, in the above-described embodiment, the distribution of the secondary air amount and the tertiary air amount is adjusted and the distribution of the secondary air increases when the volatile content of the pulverized coal increases. However, the invention is not limited to the configuration. For example, in the coal pulverizers 531, 532, 533, 534, and 535, the air amount (the transportation air amount) may be increased or decreased or the additional air amount may be increased or decreased.
Further, the boiler of the invention is not limited to the configuration of the pulverized-coal-combustion boiler 510 or the configuration or the number of the combustion burners 521, 522, 523, 524, and 525.
Further, in the above-described embodiment, as the combustion device 512, four combustion burners 521, 522, 523, 524, and 525 respectively provided in the wall surface of the furnace 511 are disposed as a five stages in the vertical direction, but the configuration is not limited thereto. That is, the combustion burner may be disposed at the corner instead of the wall surface. Further, the combustion device is not limited to the turning combustion type, and may be a front combustion type in which the combustion burner is disposed in one wall surface or an opposed combustion type in which the combustion burners are disposed in two wall surfaces so as to be opposed to each other.

Reference Signs List

510 PULVERIZED-COAL-COMBUSTION BOILER
511 FURNACE
521, 522, 523, 524, 525 COMBUSTION BURNER
537 AIR DUCT
539 ADDITIONAL AIR NOZZLE (ADDITIONAL AIR NOZZLE)
540 BRANCHED AIR DUCT
541, 542, 543, 544, 545, 546, 547, 568 FLOWRATE ADJUSTMENT VALVE (AIR AMOUNT ADJUSTING DEVICE)
548 CONTROL DEVICE
551, 552 SUPERHEATER (HEAT EXCHANGER)
553, 554 REHEATER (HEAT EXCHANGER)
555, 556, 557 ECONOMIZER (HEAT EXCHANGER)
561 FUEL NOZZLE
562 SECONDARY AIR NOZZLE
563 TERTIARY AIR NOZZLE

Claims

A boiler (510) comprising:
a furnace (511) for burning solid fuel and air;

a heat exchanger (551,552;553,554;555,556,557) for collecting heat by a heat exchange inside the furnace (511);

a fuel nozzle (561) that is arranged to blow a fuel gas obtained by mixing solid fuel with primary air into the furnace (511), wherein the fuel nozzle (561) has plural flame stabilizing members disposed as a flame stabilizer (564) inside the fuel nozzle (561) to realize an inner flame stabilization of the combustion flame;

a secondary air nozzle (562) that is arranged to blow secondary air from the outside of the fuel nozzle (561) to the furnace (511);

an additional air nozzle (539) that is arranged to blow additional air to the upper side of the fuel nozzle (561) and the secondary air nozzle (562) in the furnace (511);

a tertiary air nozzle (563) that is arranged to blow tertiary air from the outside of the secondary air nozzle (562) to the furnace (511);

an air amount adjusting device (541,542,543,544,545,546,547,568) that is arranged to adjust the amount of the air supplied to the fuel nozzle (561), the secondary air nozzle (562), the tertiary air nozzle (563), and the additional air nozzle (539); and

a control device (548) that is arranged to control the air amount adjusting device (541,542,543,544,545,546,547,568) in response to a volatile content of the solid fuel so as to adjust a distribution of the total air amount of the primary air and the secondary air, and a total air amount of the tertiary air and the additional air,

wherein the fuel nozzle (561), the secondary air nozzle (562) and the tertiary air nozzle (563) have a structure to supply the fuel gas, the secondary air and the tertiary air as a straight flow to form the combustion flame,

wherein the flame stabilizer (564) is formed in a double-cross split structure in which two flame stabilizing members following the horizontal direction and two flame stabilizing members following the vertical direction are disposed in a cross shape to divide the fuel gas passage into nine segments,

wherein widened portions are formed in front end portions of the respective flame stabilizing members downstream in the fuel gas flowing direction, and

wherein front end surfaces of the widened portions of the front end portions of the flame stabilizing members are disposed so as to be flush with an opening portion (561a) of the fuel nozzle (561).
The boiler (510) according to claim 1,
wherein the control device (548) is arranged to control the air amount adjusting device (541,542,543,544,545,546,547,568) so that the primary air amount and the additional air amount become a predetermined air amount, and to adjust a distribution of the secondary air and the tertiary air in response to the volatile content of the solid fuel.
The boiler (510) according to claim 1,
wherein the control device (548) is arranged to control the air amount adjusting device (541,542,543,544,545,546,547,568) so that the tertiary air amount and the additional air amount become a predetermined air amount while the primary air and the secondary air are fixed.
The boiler (510) according to any one of claims 1 to 3,
wherein the control device (548) is arranged to change a distribution of the secondary air and the tertiary air by increasing the secondary air amount and by decreasing the tertiary air amount when the volatile content of the solid fuel increases.
A method for operating a boiler (510) including a furnace (511) that burns solid fuel and air, a heat exchanger (551,552;553,554;555,556,557) that collects heat by a heat exchange inside the furnace (511), a fuel nozzle (561) that is arranged to blow a fuel gas obtained by mixing solid fuel with primary air to the furnace (511) and that has plural flame stabilizing members disposed as a flame stabilizer (564) inside the fuel nozzle (561) to realize an inner flame stabilization of the combustion flame, wherein the flame stabilizer (564) is formed in a double-cross split structure in which two flame stabilizing members following the horizontal direction and two flame stabilizing members following the vertical direction are disposed in a cross shape to divide the fuel gas passage into nine segments, wherein widened portions are formed in front end portions of the respective flame stabilizing members downstream in the fuel gas flowing direction, and wherein front end surfaces of the widened portions of the front end portions of the flame stabilizing members are disposed so as to be flush with an opening portion (561a) of the fuel nozzle (561), a secondary air nozzle (562) that is arranged to blow secondary air from the outside of the fuel nozzle (561) into the furnace (511), a tertiary air nozzle (563) that is arranged to blow tertiary air from the outside of the secondary air nozzle (562) into the furnace (511), and an additional air nozzle (539) that is arranged to blow additional air to the upper side of the fuel nozzle (561) and the secondary air nozzle (562) in the furnace (511), wherein the fuel nozzle, the secondary air nozzle and the tertiary air nozzle have a structure to supply the fuel gas, the secondary air and the tertiary air as a straight flow to form the combustion flame, wherein a distribution between a total air amount of the primary air and the secondary air and a total air amount of the tertiary air and the additional air is adjusted in response to a volatile content of the solid fuel.
The method for operating the boiler (510) according to claim 5,
wherein the distribution of the secondary air and the tertiary air is changed by increasing the secondary air amount and by decreasing the tertiary air amount when the volatile content of the solid fuel is increased.